The present invention relates generally to the field of orthodontics, and more particularly to dental repositioning appliances having improved or optimized geometries incorporating one or more shaped features or protrusions.
An objective of orthodontics is to move a patient's teeth to positions where function and/or aesthetics are optimized. Traditionally, appliances such as braces are applied to a patient's teeth by an orthodontist or dentist and the set of braces exerts continual force on the teeth and gradually urges them toward their intended positions. Over time and with a series of clinical visits and adjustments to the braces, the orthodontist adjusts the appliances to move the teeth toward their final destination.
More recently, alternatives to conventional orthodontic treatment with traditional affixed appliances (e.g., braces) have become available. For example, systems including a series of preformed aligners have become commercially available from Align Technology, Inc., Santa Clara, Calif., under the tradename Invisalign® System. The Invisalign® System is described in numerous patents and patent applications assigned to Align Technology, Inc. including, for example in U.S. Pat. Nos. 6,450,807, and 5,975,893, as well as on the company's website, which is accessible on the World Wide Web (see, e.g., the url “align.com”). The Invisalign® System includes designing and/or fabricating multiple, and sometimes all, of the aligners to be worn by the patient before the aligners are administered to the patient and used to reposition the teeth (e.g., at the outset of treatment). Often, designing and planning a customized treatment for a patient makes use of computer-based 3-dimensional planning/design tools, such as software technology available from Align Technology, Inc. The design of the aligners can rely on computer modeling of a series of planned successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and elastically reposition the teeth to each of the planned tooth arrangements.
Orthodontic appliances, in general, apply force and torque on a tooth crown to move teeth, with the applied force typically normal with respect to the surface of a tooth or attachment positioned on the tooth. The tooth root and/or other anatomical structures may hinder the desired tooth movement and render the center of resistance down below the gingival line and in the tooth bone socket, which can make certain movements difficult to accomplish by application of force to the tooth crown. If a translational movement is desired, for example, the translational force is optimally applied through the center of resistance or with sufficient counterbalancing forces, otherwise force on the tooth crown by an appliance can cause unwanted torque with respect to the center of resistance. Clinically, the unwanted torque can result in unwanted tooth movement and root movement, thereby decreasing the effectiveness of the treatment. As appliances are designed to contact and apply forces to the crown of the tooth, and the tooth center of resistance lies below the gingival line, applying forces more directly about the center of resistance is difficult with existing appliances. Accordingly, improved appliances and techniques are needed for applying more effective tooth movement forces to the teeth during orthodontic treatment, and reducing unwanted tooth movements.